The present invention relates to data storage, and more particularly, to reliable data reading with data set screening by error injection using a data channel in a magnetic tape drive.
With a linear tape storage system, it is important to keep magnetic data heads aligned with target data tracks while reading data from tape media. A track-following servo system is usually engaged with controlling the magnetic head position using a position error signal (PES) which is derived from positional relativity between the pre-written servo pattern on the magnetic media and magnetic head position. In order to follow the servo track, a valid PES must be detected. However, tape media typically have some amount of defects and scratches of varying sizes, particularly after being in use for any significant amount of time. Detecting an invalid PES causes loss of magnetic head position control in a feedback loop and eventually data readers will become located outside of target data tracks.
On the other hand, magnetic heads may be knocked off track while in operation due to a mechanical disturbance, vibration, and/or shock event. Any of these disturbances has the potential to push magnetic head position off of the target tracks.
In either case, off-track reading causes increases in read errors which must be responded to by the tape drive. To ensure data integrity, the tape drive adds error correction code (ECC) to original data while writing the data onto tracks of the tape media. The ECC and associated data is then decoded for reconstruction of the original data during a read operation. The ECC contributes to more successful data recovery in case the original data is damaged due to media defect or some other disturbance. It also helps to compensate for off-track reading, but its effectiveness depends on the severity of the off-track reading.